1. Field of the Invention
The present invention relates to a dielectric resonator apparatus, a method for adjusting a coupling coefficient of a dielectric resonator apparatus, and a manufacturing apparatus for manufacturing a dielectric resonator apparatus, and in particular, a TM dual mode dielectric resonator apparatus, a method for adjusting a coupling coefficient between two dielectric resonators of a TM dual mode dielectric resonator apparatus, and a manufacturing apparatus for manufacturing TM dual mode dielectric resonator apparatus.
2. Description of the Related Art
FIG. 5 shows a conventional TM dual mode dielectric resonator apparatus 51 comprising a cross-shaped TM dual mode dielectric resonator 52, which is disclosed in the Japanese patent Laid-open publication No. 63-313901.
Referring to FIG. 5, in the conventional TM dual mode dielectric resonator apparatus 51, there is provided or mounted the TM dual mode dielectric resonator 52 within an electrically conductive case 53 which functions as a waveguide. The TM dual mode dielectric resonator 52 is made of a dielectric ceramics material, and is constituted by integrally forming two TM mode rectangular-cylinder-shaped dielectric resonators 54 and 55 in a shape of a cross so that the longitudinal direction of the dielectric resonator 54 is perpendicular to that of the dielectric resonator 55. Further, the case 53 is constituted by forming electrically conductive electrodes 57 on all the surfaces of a case main body 56 made of a dielectric ceramics material by plating the case with a metal paste, by a vapor deposition method for depositing a thin metal film on the case or by another method, and the case main body 56 is formed integrally and simultaneously with the TM dual mode dielectric resonator 52. In a crossing portion of the two dielectric resonators 54 and 55 (referred to as a crossing portion hereinafter) formed in a shape of the cross of the TM dual mode dielectric resonator 52, coupling grooves 58 for coupling an operation mode of the dielectric resonator 54 with that of the dielectric resonator 55 are formed so as to have longitudinal lengths each from the front surface of the dielectric resonators 54 and 55 to the back surface thereof, and so as to have depths each extending from two corners of the crossing portion which oppose each other towards the center of the crossing portion in a diagonal direction of the crossing portion.
As shown in FIG. 5, the following electric lines of force are in the TM dual mode dielectric resonator 52:
(a) electric lines E.sub.1 and E.sub.2 of force of the respective dielectric resonators 54 and 55 parallel to respective longitudinal directions thereof which are indicated by alternate long and short dash lines; PA1 (b) electric lines Ee of force of the even mode extending from the left end of the dielectric resonator 54 through the crossing portion of the two dielectric resonators 54 and 55 to the top end of the dielectric resonator 55 and vice versa, and also extending from the bottom end of the dielectric resonator 55 through the crossing portion to the right end of the dielectric resonator 54 and vice versa, which are indicated by dotted lines; and PA1 (c) the other electric lines Eo of force of the odd mode extending from the right end of the dielectric resonator 54 through the crossing portion to the top end of the dielectric resonator 55 and vice versa, and also extending from the bottom end of the dielectric resonator 55 through the crossing portion to the left end of the dielectric resonator 54 and vice versa, which are indicated by solid lines, PA1 wherein the electric lines E.sub.1 of force are generated by the dielectric resonator 54, the electric lines E.sub.2 of force are generated by the dielectric resonator 55, and the electric lines Ee and Eo are generated in the TM dual mode dielectric resonator 52 shown in FIG. 5. PA1 an electrically conductive case; PA1 a cross-shaped TM dual mode dielectric resonator provided in said case, said TM dual mode dielectric resonator comprising first and second dielectric resonators integrally formed so as to be perpendicular to each other; and PA1 at least one coupling groove for coupling an operation mode of said first dielectric resonator with an operation mode of said second dielectric resonator, formed on at least one of a front surface and a back surface of a crossing portion of said first and second dielectric resonators, in a diagonal direction of said crossing portion so as to cut electric lines of force of either one of an odd mode and an even mode. PA1 at least one coupling projection for coupling an operation mode of said first dielectric resonator with an operation mode of said second dielectric resonator, formed on at least one of a front surface and a back surface of a crossing portion of said first and second dielectric resonators, in a diagonal direction of said crossing portion so as to disturb electric lines of force of either one of an odd mode and an even mode. PA1 adjusting the coupling coefficient between said first and second dielectric resonators by changing the depth of said at least one coupling in a direction towards front and back surfaces of said case. PA1 wherein said manufacturing apparatus comprises: PA1 a pair of main molds each having a cavity for forming said TM dual mode dielectric resonator and a penetrating hole formed in the center of said cavity so as to penetrate said main mold; and PA1 a pair of sub-molds formed so as to insert said penetrating hole, said sub-molds being slid in said penetrating hole in a direction towards front and back surfaces of said case so that the height of projection of said sub-mold into said cavity can be changed. PA1 wherein said manufacturing apparatus comprises: PA1 a pair of main molds having a cavity for forming said TM dual mode dielectric resonator and a penetrating hole formed in the center of said cavity so as to penetrate said main mold; and PA1 a pair of sub-molds formed so as to insert said penetrating hole, said sub-molds being slid in said penetrating hole in a direction towards front and back surfaces of said case so that the depth of said sub-mold pulled-into said cavity can be changed.
As shown in FIG. 5, since the two grooves 58 are formed in the two corners opposing each other in a diagonal direction of the crossing portion of the TM dual mode dielectric resonator 52, the effective dielectric constant in the odd mode in which the electric lines Eo of force pass through the grooves 58 is different from that in the even mode in which the electric lines Ee of force pass through a portion where no groove 58 is formed, and thus a coupling is caused between the operation modes of the two dielectric resonators 54 and 55.
For the mass production of the conventional TM dual mode resonator apparatus 51, a dielectric ceramics molded body comprised of both the TM dual mode dielectric resonator 52 and the case main body 56 of the dielectric resonator apparatus 51 having the above-mentioned structure is formed using a pair of molds 59 (see FIG. 6).
FIG. 6 is a perspective view of one mold 59 of a pair of molds, and another mold (not shown) has a symmetrical shape with respect to a mold opening surface 60, wherein there is formed a space for forming the molded body between a pair of molds 59. Referring to FIG. 6, reference numeral 61 denotes a cavity of a rectangular-ring-shaped concave shape for forming the case main body 56 which is formed in the inner peripheral portion of the mold 59, reference numeral 62 denotes a cavity of a cross-shaped concave shape for forming the TM dual mode dielectric resonator 52 which is formed in the inner side of the cavity 61, and reference numeral 63 denotes projections for forming the coupling grooves 58 which are formed so as to project from inner projections 64 towards the center of the cavity 62 in a diagonal direction thereof.
In the TM dual mode dielectric resonator 52 provided in the above-mentioned dielectric resonator apparatus 51, a coupling coefficient between both the dielectric resonators 54 and 55 can be adjusted by changing the respective depths in the diagonal direction of the coupling grooves 58. However, the adjustment of the depths of the coupling grooves 58 is performed by cutting inner walls of the coupling grooves 58 after firing the dielectric ceramics molding body or after manufacturing the dielectric resonator apparatus 51. This cutting process takes a long time.
Further, in the case of manufacturing a plurality of kinds of dielectric resonator apparatus 51 having coupling coefficients different from each other, it is required to use a number of molds 59 corresponding to the number of kinds of dielectric resonator apparatus 51. This results in an expensive manufacturing cost of the molds 59.
Furthermore, since the opening direction of a pair of molds 59 is substantially perpendicular to the depth direction of the coupling grooves 58, it is difficult to remove the coupling grooves 58 from the molds 59, and further it is difficult to design the molds 59.